As semiconductor technology is developing continuously, the characteristic lengths of devices have constantly reduced from micron to the current nanometer scale; and, the corresponding material system structures used have also changed from the traditional higher dimensions (three-dimensions) to lower dimensions (two-dimensions, quasi-one-dimension and one-dimension). Devices based on the low dimensional semiconductor structure usually have a simple process, are easy to integrate, and small in stray capacitance, and therefore are taken as an ideal choice for high-frequency devices.
Besides, in comparison with the three-dimensional conductive structures, low dimensional conductive structure's shielding effects on the electric field are greatly reduced, which results in strong electric field distribution around the conductive structure and increased electric field coupling among the conductive structures. Due to this characteristic of the low dimensional conductive structure, a so-called “self-gating effect” appears in the “Y” shaped planar nano-switch (J. Jan-olof and J. Wesström, “Self-Gating Effect in the Electron Y-Branch Switch”, Phys. Rev. Lett. 82, 2564 (1999)).
Frequency multiplying technology is always an essential constitutive part of wireless communication and broadcasting technology. With the rapid development of science and technology, frequency multiplying technology is becoming more and more important. At present, various fields such as digital communication, analog communication, radio astronomy, and terahertz science technologies all have huge demands on frequency multiplying technology. Non-linear elements will result in distortion in waveform of the input signals. According to the Fourier transform theory, the frequency ingredients of the output signal will change. This is the well-known physical basis of the generation of frequency multiplication. At present, non-linear frequency multipliers mainly includes two major types: frequency multipliers based on diodes, and those based on field effect transistors. Those frequency multipliers have a common feature that the output signal includes various frequency ingredients, thus additional filter circuits are needed.
MIT researchers published the first frequency multiplier which consists of a single field effect transistor and needs no additional filter circuit (H. Wang, D. Nezich, J. Kong and T. Palacios, “Graphene frequency multipliers”, IEEE Electron Device Letters 30, 547 (2009)). This frequency multiplier is also based on the non-linear feature of the field effect transistor, but the material for manufacturing the field effect transistor is not a traditional material, but a novel material with unique electric properties—graphene. The field effect transistor made from this novel material has a special “V” type current-voltage characteristics such that the output signals only contain the second harmonics of the input signal, thus a single graphene field effect transistor can be manufactured into the frequency multiplier without an additional filter circuit.
The above publication from the MIT researchers greatly reduces the circuits of the frequency multiplier, however, this invention is based on the unique electric properties of the manufacturing material, which means that this invention is strongly material depended and cannot be achieved by using other material systems.